Blastomyces dermatitidis, a thermally dimorphic fungus, is a pulmonary pathogen in humans, 14 dogs, 5,6 mice, 7,8 and other mammals. 7 Untreated disseminated-human blastomycosis has been reported to have a mortality rate greater than 80%. 9 However, virulent and avirulent isolates of B. dermatitidis have been described 8,10,11 and in five outbreaks, blastomycosis in some patients (28 of 46) resolved without therapy. 4 Blastomycosis is naturally acquired by way of the pulmonary route 12 by inhalation of the infectious agent in its saprophytic or mycelial-conidia phase. Five documented point outbreaks, summarized by Sarosi et al. 3 and Tenenbaum et al., 4 have been associated with construction activity and postulated disturbance of B. dermatitidis in its ephemeral ecological niche. 13-16 Although the dog was the first animal used in the study of blastomycosis 17 and in later epidemiological studies, 5,6 the laboratory mouse has been 81the animal of choice for isolation of B. dermatitidis from nature 13,14 and development of an animal model of pulmonary blastomycosis. 8 The murine model of pulmonary blastomycosis has been used extensively over the past several years for immunological 18,21 and drug treatment studies, 22,23 consequently it will be described first and in detail.